Method and device for treating suspected errors

ABSTRACT

A method and a device for producing an error signal and carrying out measures based thereon in a motor vehicle equipped with a wheel-slip control system and/or a wheel deceleration control system. At least one function variable representing the functionality of the wheel-slip control system and/or wheel-deceleration control system is monitored here for an error and if at least one error is detected, the value of at least one error counter is incremented. Likewise when there is at least one detected error, at least one error signal is output when the value of at least one error counter exceeds a predeterminable limiting value. For at least one error counter, at least two different, predeterminable limiting values coexist simultaneously, and when each of these is exceeded by the counter reading of the at least one error counter, different error signals are output, and in response to the different error signals, different measures are carried out in the wheel-slip control system and/or wheel deceleration control system.

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device for producing an error signal in a motor vehicle having the features of the preamble of the independent claims.

[0002] In German Patent Application 196 38 280 A1, producing an error signal in a motor vehicle having at least two right and left wheels situated in the rear and front region of the vehicle is described. To this end, signals representing the rotational speeds of the wheels of the vehicle are recorded. In particular, depending on the signals recorded, the presence of cornering is furthermore recorded. The signals recorded during cornering are then compared according to the invention with a specified behavior existing during cornering, whereupon the error signal is produced, depending on the comparison. Through the comparison, it is possible to detect incorrect rotational speed sensor signals as a result of incorrectly connecting the wires, for example.

[0003] A device and a method of monitoring sensors in a vehicle is known from German Patent Application 196 36 443 A1. Here, the device according to the invention monitors sensors in a vehicle, which produce signals that each represent different physical variables. The device contains means with which comparative variables equally defined for the sensors are determined for at least two sensors, based on at least the signals they produced. Furthermore, the device contains other means with which a reference variable is determined, based on at least the comparative variables determined. Monitoring is carried out in the monitoring means at least for one sensor based on at least the reference variable determined. Aside from the monitoring means, the device contains additional means, with which at least for one sensor a correction of the signal it produces is carried out at least based on the reference variable. The features of the preamble of the independent claims arise from German Patent Application 196 38 280 A1.

ADVANTAGES OF THE INVENTION

[0004] The present invention relates to a method and a device for treating a suspected error. It is based on a method of producing an error signal and carrying out measures based thereon in a motor vehicle equipped with a wheel-slip control system and/or a wheel deceleration control system, which

[0005] monitors for an error at least one function variable representing the function of the wheelslip control system and/or wheel-deceleration control system, and

[0006] increments the value of at least one error counter if at least one error is detected, and

[0007] outputs at least one error signal when the value of at least one error counter exceeds a predeterminable limiting value.

[0008] The essence of the present invention is that

[0009] for at least one error counter, at least two different, predeterminable limiting values coexist simultaneously, and when each of these is exceeded by the counter reading of the at least one error counter, different error signals are output, and

[0010] in response to the different error signals, different measures are carried out in the wheelslip control system and/or wheel deceleration control system.

[0011] As a result, graduated measures are allowed in the event of a suspected error. In the following, the term “wheel-slip control system” will be frequently used for a clearer description. This always refers to a wheel-slip control system and/or wheel deceleration control system, however.

[0012] To illustrate, one imagines that a monitoring device in a wheel-slip control system of a motor vehicle has detected a possible error. At the same time, however, the probability of there actually being an error is not so great as to justify drastic countermeasures, such as the automatic shutdown of the wheel-slip control system. In this case, the present invention allows graduated countermeasures to be carried out. For example, when an error is detected once, pressure build-up or pressure reduction procedures affected by the wheel-slip control system may be slowed down. More drastic countermeasures are taken if the error is detected again or repeatedly. Instead of pressure build-up and pressure reduction procedures, general braking force buildup and braking force reduction procedures may of course also be slowed down. The electromechanical brakes (EMB) come to mind here, for example, in which the braking force buildup and breaking force reduction are no longer hydraulically controlled. The present invention is therefore also easily applicable to vehicles equipped with an electromechanical brake system.

[0013] An advantageous operative range of the present invention is then provided when the wheelslip control system is a vehicle dynamics control system, which regulates at least one variable representing the vehicle dynamics toward a desired behavior.

[0014] It is furthermore an advantage when the monitoring of at least one function variable representing the function of the wheel-slip control system takes place such that a verification of the fulfillment of at least one given condition takes place.

[0015] As already mentioned, a slowing down in the wheel brakes of the pressure build-up dynamics is advantageously performed as the first measure when the lowest limiting value is exceeded by one error counter.

[0016] It can in effect be generalized (for example, for the electromagnetic brake) that a slowing down of the braking force buildup procedure and braking force reduction procedure is performed in the wheel brakes as the first measure when the lowest limiting value is exceeded by one error counter.

[0017] As the second measure, for example, when the second lowest limiting value is exceeded by one error counter, the intervention threshold for at least one brake intervention of the vehicle dynamics control systems is increased and/or at least one intervention of the vehicle dynamics control systems is completely prohibited.

[0018] In other words, this means that for example as a second measure, when the second lowest limiting value is exceeded by one error counter, a greater deviation of at least one variable representing the vehicle dynamics from its desired behavior is permitted before a control intervention of the vehicle dynamics control system takes place and/or as a second measure at least one control intervention of the vehicle dynamics control system is completely prohibited. Prohibiting a control intervention by a vehicle dynamics control system may mean here that at least one type of intervention is completely prohibited, for example an intervention against oversteering or an intervention against understeering or an intervention on a selected wheel.

[0019] A further monitoring measure may be as follows: the monitoring of at least one function variable takes place such that a variable represented by the output signal of a vehicle sensor is compared with a variable calculated through a mathematical model.

[0020] The advantage here is when a variable represented by the output signal of a vehicle sensor is compared only during certain driving states to a variable calculated through a mathematical model. This is related to the validity range of the mathematical model. If the vehicle is in a driving state in which the mathematical model is not valid, then the variable calculated through the mathematical model will also no longer have any substantial significance.

[0021] A function variable is advantageously understood as the voltage at one point of the electronic circuit of the wheel-slip control system and/or wheel deceleration control system. However, this may also be understood as the output signal of a sensor or a variable calculated from a mathematical model.

[0022] Other advantageous embodiments of the present invention are to be derived from the subordinate claims.

DRAWING

[0023] An exemplary embodiment of the present invention is illustrated and explained in the following drawing. The drawing is made up of FIGS. 1 to 4.

[0024]FIG. 1 shows the principle sequence of the method for treating a suspected error.

[0025]FIG. 2 shows a simple safety concept for a wheel-slip control system, in which the wheel-slip control system is switched off in the event of a known error.

[0026]FIG. 3 shows a first safety concept for a wheel-slip control system, in which a suspected error is already detected before the error detection, and in response thereto, the pressure build-up dynamics in the wheel brakes is slowed down in the course of brake applications induced by the wheel-slip control system.

[0027]FIG. 4 shows a second safety concept for a wheel-slip control system, in which a suspected error is already recognized before the error detection, and in response thereto, the intervention thresholds of the vehicle dynamics control system are extended.

EXEMPLARY EMBODIMENTS

[0028] First, some possible monitoring measures on a wheel-slip control system are presented:

[0029] 1. Hardware monitoring: The monitoring of the voltage level at one point of the electronic circuit is conceivable here, for example.

[0030] 2. Sensor monitoring: Since a wheel-slip control system also includes sensors (for example, wheel speed sensors, a transverse acceleration sensor, a steering angle sensor, a yaw rate sensor, pressure sensors, etc.), monitoring of the sensors is conceivable. For instance, the output signal sent by a sensor may be monitored to find out whether the value of this signal or of the variable represented by this signal lies in a physically reasonable or possible range. Monitoring of the change over time of a variable represented by a sensor signal is also conceivable.

[0031] 3. Model-supported monitoring: Some variables are two-fold. They are recorded by a sensor, and they are determined from a mathematical model. A comparison of the variable obtained from the sensor signal with the variable determined from a mathematical model is provided here. In the process, the scope of validity of the mathematical model should of course be observed, meaning that a comparison during a driving state in which the mathematical model is not valid only has limited significance.

[0032] Separate error counters are allocated to different, fundamentally possible errors. The fundamental procedure with respect to error counter k, which carries out a monitoring k, is illustrated in FIG. 1. Aside from error counter k, there are other error counters 1, 2, 3, . . . , k−1, k+1, . . . , N, which carry out monitorings 1, 2, . . . , k−1, k+1, . . . , N. There are N error counters provided altogether.

[0033] Block 100 represents a signal source k, which sends one or more output signals to block 102 for monitoring. This signal source may be a sensor, for example, or the voltage at a particular point in the electronic circuit of the wheel-slip control system, or the output signal of a mathematical model. The output variable(s) sent by this signal source k is/are monitored in block 102. There is a monitoring inquiry k for this purpose. Through this monitoring inquiry, it may be verified, for example, whether the output variable sent by signal source k is greater than a predeterminable limiting value. However, more complicated inquiries are also conceivable. For instance, it may be verified whether the output variable sent by signal source k is greater than a first predeterminable limiting value (=minimum value) and at the same time smaller than a second predeterminable limiting value (=maximum value).

[0034] It is also conceivable for signal source k to send multiple output signals, for example the output voltage to a connecting terminal of the wheel-slip control system as well as the temperature at a particular point of the wheel-slip control system. Combined monitoring inquiries are also consequently conceivable. Such a monitoring inquiry could involve verifying whether the temperature falls below a particular, predeterminable value and at the same time whether a voltage simultaneously exceeds another predeterminable value, for example.

[0035] Another combined monitoring inquiry could involve a comparison between the variable obtained from a sensor signal and the variable determined from a mathematical model.

[0036] According to a flow chart, block 100 may also be interpreted as reading in data. The type of this data was illustrated in the previous paragraph.

[0037] If monitoring inquiry 102 shows that the signal sent by signal source 100 fulfills all the conditions, i.e., it is plausible, error counter ik in block 101 is reset to zero. Error counter ik contains the number of times that monitoring inquiry k was not fulfilled as determined within an uninterrupted sequence. Afterwards, the output signals of signal source 100 are monitored anew, i.e., at least one variable is read in.

[0038] However, if monitoring inquiry 102 shows that the output signal (or output signals) from block 100 does not fulfill all the required conditions, there may be an error. For this reason, value ik of the error counter is increased by one in block 103. An inquiry as to whether ik>N1 takes place in block 104. Here, N1 is a predeterminable limiting value. If this condition is not fulfilled, then there is a branching back to block 100. If this condition is fulfilled, the next verification of ik follows in block 105: ik>N2.

[0039] Here, N2 is greater than N1.

[0040] If the condition in block 105 is not fulfilled, it means that ik is greater than N1 but less than N2. First measures are now therefore initiated in block 106. These first measures may involve a slowing down of the pressure build-up dynamics or pressure reduction dynamics of the wheel-slip control system, for example. Instead of pressure build-up and pressure reduction, these may be power buildup and power reduction, as is the case in the electromechanical brake.

[0041] This fact should once again be explained briefly and clearly:

[0042] Through ik>N1, it was detected that there was probably an error in the wheel-slip control system.

[0043] But because ik is even less than N2, it is not yet quite certain that there is really an error.

[0044] The first measures described are therefore initiated, for example.

[0045] The point of the first measures lies in the example that the wheel-slip control system continues to perform all the necessary interventions, albeit somewhat slower. As a result, time is gained for a further verification of the suspected error.

[0046] However, if ik>N2 in block 105, a further inquiry ik>N3 subsequently follows in block 107. Here, N3>N2.

[0047] If ik is not greater than N3, second measures are initiated in block 108 that advantageously have even somewhat greater effects on the wheel-slip control system. In the example of a vehicle dynamics control system (ESP, FDR), this may mean that the intervention thresholds of some control interventions are increased or that some interventions are even completely prohibited.

[0048] If it is determined in block 107 that ik>N3, third measures are initiated in block 109. These third measures may involve relevant functions of the wheel-slip control system being switched off or even the entire wheel-slip control system being switched off, for example. If ik>N3, there is a strong likelihood of an error in the wheel-slip control system or in a component. Block 109 is connected to block 100 through a broken line. This has to do with the fact that a new monitoring cycle may begin again in block 100. However, it is also possible to dispense with further monitorings in a completely switched off wheel-slip control system.

[0049] As already mentioned, there are separate error counters for separate errors. The method illustrated in FIG. 1 is also logically transferable to the other error counters. In a particular embodiment, it is possible for each of the first measures carried out to be identical when different counter errors have reached the appropriate limiting values. The same also applies to the second and third measures.

[0050] However, it is also conceivable to carry out different measures, depending on the type of error detected (i.e., by the error counter).

[0051] Furthermore, it is possible to individually select limiting values N1, N2 and N3 for all error counters. As a result, for non-serious errors it is possible to select higher intervention limiting values N1, N2 and N3 than for serious errors, for example. However, it is also conceivable for N1, N2 and N3 to assume the same values for all error counters.

[0052] In FIG. 1, the first, second, and third measures were taken as an example, depending on the status of the error counter. It is conceivable to make the measures even more precisely graduated, i.e., there are still fourth measures, fifth measures, etc. However, it is also possible and conceivable to make do with only two graduated measures.

[0053] Concrete embodiments of the safety concept discussed in general in FIG. 1 are illustrated in FIGS. 2 to 4. Since these figures are all quite similarly designed, the general design should first be explained. This assumes a wheel-slip control system designed as a vehicle dynamics control system.

[0054] Each of these figures is made up of two diagrams. In the upper diagram, different variables a(t) (ordinate) are respectively plotted as a function of time t (abscissa). This will now be explained in order.

[0055] The topmost signal 200 describes the state of the pump motor of the wheel-slip control system as a binary signal course. This is the motor of the return pump, which provides the active pressure build-up (i.e., without assistance from the driver). If this signal assumes its ‘low’ value, the pump motor is switched off If the signal assumes the ‘high’ value, the pump motor is switched on.

[0056] As the next signal, the yaw rate vGi measured with a yaw rate sensor is plotted. This is assumed to be constant over time in all cases, i.e., there is a horizontal straight line. The curly bracket 210 indicates the hatched range specifying the allowed controller tolerance range of the yaw rate. This concept will be discussed later in greater detail.

[0057] As a third signal from above, yaw rate vGiLw calculated via a mathematical model is drawn with broken lines. The single-track model, also known as the Ackermann Function, is suitable as a mathematical model, for example. The yaw rate is computed therein from the steering angle, the vehicle longitudinal velocity, as well as other parameters.

[0058] As a fourth and final signal from above, variable p is drawn in as a function of time p is a measure of the built-up pressure in a selected wheel brake cylinder.

[0059] In the lower of the two diagrams, the measured yaw rate vGi, the computed yaw rate vGiLw, as well as the controller tolerance range of the yaw rate in hatched pattern are again drawn in. The controller tolerance range in the ordinate direction is somewhat narrower than illustrated in the upper diagram. This is for reasons of clarity. However, the state of error counter F(t) was included as additional curve 220. In this case, the state of the error counter was shown as a continuously rising straight line for reasons of clarity. The state of the error counter is preferably a discrete, whole number, i.e., this may also be a step function. This distinction is irrelevant for the following considerations, however.

[0060]FIG. 2 must first be discussed. To this end, measured yaw rate vGi is first compared in the upper diagram with computed yaw rate vGiLw. The validity of the mathematical model is required over entire time axis t for computing yaw rate vGiLw. At time t1, a sensor error 230 (see lightning symbol in the lower diagram) of the steering angle sensor, for example, occurs. It is assumed that the steering angle enters into the computation of yaw rate vGiLw. A sudden deviation between vGi and vGiLw therefore occurs at time t 1. This deviation is so great that vGiLw even drops out of the controller tolerance range of yaw rate vGi. This has two consequences:

[0061] 1. The vehicle dynamics control system erroneously detects a deviation between the setpoint and the actual yaw rate. A control intervention is thus started, recognizable by the switching on of the pump as well as by the accretion of pressure p in the upper diagram.

[0062] 2. Value F(t) of the error counter allocated to this error in the lower diagram begins to rise. This has to do with the fact that with every repeated monitoring (see FIG. 1, block 102), a difference between the two yaw rates (vGi and vGiLw), and, consequently, another suspected error, is determined. At time t=t2, the value of the error counter has reached the value F1, i.e., the error is deemed detected with enough certainty. This is indicated by lightning symbol 240. The control intervention of the vehicle dynamics control system is therefore terminated again at time t2. For that, pump 200 is switched off and pressure p again tapers off.

[0063] Lightning symbol 230 also appears in FIGS. 3 and 4 with the same meaning.

[0064] In FIG. 3, lightning symbol 250 is drawn in in addition to time t3 (with t3<t2). At time t3, the error counter has already reached a first limiting value F2. The dynamic restriction of the pressure is therefore activated at time t3 (first measure). This may be seen in the increase in pressure in the upper diagram, which is more gradual than in FIG. 2. This means that the control intervention of the vehicle dynamics control system is taking place at a slower pace. At time t2, the error counter has even reached the second (and higher) limiting value F 1. A positive error has now been detected and pressure p is again reduced. As a result of the previous first measure, only a little pressure needs to be reduced. The effects of the erroneous brake application of the vehicle dynamics control system have remained weaker than in FIG. 2.

[0065] A further embodiment of the present invention is illustrated in FIG. 4. At time t1, the control intervention of the vehicle dynamics control system begins again erroneously. This may be seen in the upper diagram in pressure p, which has started to increase. The counter error reaches value F3 at time t4. A suspected error is detected, characterized by lightning symbol 260. As a result of the suspected error, an extension of the intervention threshold of the vehicle dynamics control system takes place. This is drawn with a hatched pattern in the upper diagram and marked with the curly bracket 211. Since the control tolerance range of the vehicle dynamics control system has now become wider, the computed value vGiLw for t>t4 once again falls within the control tolerance range of vGi. The intervention of the vehicle dynamics control system is therefore cancelled. This may be seen in the pressure reduction in the upper diagram. At the same time, the pump is again switched off. At time t5, the value of the error counter exceeds a second limiting value. This is marked by lightning symbol 270. The error is now deemed detected with certainty and second measures are initiated.

[0066] As already mentioned, the most varied error counters for the most varied monitoring measures are conceivable. Not only may a detected error advantageously be used to limit the functions of the wheel-slip control system, but the cause of the error may possibly be directly determined and logged, stored, or output as driver information in some conceivable form. This facilitates a subsequent diagnosis, for example during a service inspection, and results in shortened service visits. This may bring about considerable cost savings.

[0067] In the present invention, it is helpful to distinguish between two types of errors:

[0068] 1. Component errors are the errors that may clearly be allocated to one component.

[0069] 2. System errors are errors whose cause cannot be clearly determined.

[0070] The information on whether it is a component or a system error should therefore be advantageously allocated to each error counter. This information should be available for subsequent diagnosis.

[0071] Should an error that has been detected at least once suddenly no longer appear in the next monitoring (see block 102 in FIG. 1), the error counter is reset to zero in FIG. 1 in block 101.

[0072] Alternatively, there is also the following possibility for resetting the error counter:

[0073] counting with the error counter always takes place within an ignition cycle.

[0074] when a monitoring-specific suspected error occurs, the error counter is incremented by a predeterminable value, e.g., 1024. Since this is often implemented as a filter, the use of a number associated with the filter is recommended.

[0075] if the suspected error is not reset, the error counter is decremented each time by one bit in a 5.12-second pattern, for example. This means that after a time of 1024*5.12 seconds (approximately 1.5 hours), a suspected error that has been set once is forgotten.

[0076] The present invention has a particularly useful operative range in motor vehicles equipped with an electrohydraulic brake. This has much shorter response times than a conventional hydraulic brake. A control intervention of a vehicle dynamics control system is then noticeable to the driver when a brake pressure of approximately 20 bar has built up. A conventional hydraulic brake system needs about 200 milliseconds for this, while an electrohydraulic brake system only needs 20 milliseconds. Shortened error detection times are therefore particularly advantageous here. The proposed multistage error detection method facilitates robust error detection almost regardless of the speed of the actuators.

[0077] Finally, the most important points of the present invention should be summarized:

[0078] The method is based on the concept of responding to a two-stage or multistage suspected error at the start of the error detection time.

[0079] In the first stage of suspecting an error, the pressure build-up dynamics is limited. The effects of possible erroneous interventions (until the second stage of the suspected error is set) are consequently reduced.

[0080] In the second stage of suspecting an error, the vehicle controller intervention thresholds are extended. With this measure, vehicle control interventions are suppressed and time is gained for robust and certain detection of the error.

[0081] Since there is more time for error detection (longer error detection time), it is easier to clearly allocate system errors to component errors.

[0082] Counting the occurrence of a suspected error also allows the recording of errors caused by a loose connection. 

What is claimed is:
 1. A method for producing an error signal and carrying out measures based thereon in a motor vehicle equipped with a wheel-slip control system and/or a wheel deceleration control system, which monitors for an error at least one function variable representing the functionality of the wheel-slip control system and/or wheel deceleration control system, and increments the value of at least one error counter (ik) if at least one error is detected, and outputs at least one error signal when the value of at least one error counter exceeds a predeterminable limiting value (N1, N2, N3), wherein for at least one error counter, at least two different, predeterminable limiting values (N1, N2, N3) coexist simultaneously, and when each of these is exceeded by the counter reading of the at least one error counter (ik), different error signals are output, and in response to the different error signals, different measures are carried out in the wheel-slip control system and/or wheel deceleration control system.
 2. The method as recited in claim 1, wherein the wheel-slip control system and/or wheel deceleration control system is a vehicle dynamics control system, which regulates at least one variable representing the vehicle dynamics toward a desired behavior.
 3. The method as recited in claim 1, wherein the monitoring of at least one function variable representing the functionality of the wheel-slip control system and/or the wheel deceleration control system takes place such that a verification of the fulfillment of at least one given condition takes place.
 4. The method as recited in claim 1, wherein a slowing down of the braking force buildup procedure and/or braking force reduction procedure is performed in the wheel brakes as the first measure when the lowest limiting value (N1) is exceeded by one error counter.
 5. The method as recited in claim 4, wherein as a second measure when the second lowest limiting value (N2) is exceeded by one error counter, a greater deviation of at least one variable representing the vehicle dynamics from its desired behavior is permitted before a control intervention of the vehicle dynamics control system takes place, and/or as a second measure at least one control intervention of the vehicle dynamics control system is completely prohibited.
 6. The method as recited in claim 3, wherein the monitoring of at least one function variable takes place such that a variable represented by the output signal of a vehicle sensor is compared with a variable calculated through a mathematical model.
 7. The method as recited in claim 6, wherein a variable represented by the output signal of a vehicle sensor is compared only during certain driving states to a variable calculated through a mathematical model.
 8. The method as recited in claim 1, wherein a function variable is understood as the voltage at one point of the electronic circuit of the wheel-slip control system and/or wheel deceleration control system or the output signal of a sensor or a variable calculated from a mathematical model.
 9. A device for producing an error signal and carrying out measures based thereon in a motor vehicle equipped with a wheel-slip control system and/or wheel deceleration control system, which has monitoring means that monitor for an error at least one function variable representing the functionality of the wheel-slip control system and/or wheel-deceleration control system, and error counting means, in which the value of at least one error counter (ik) is incremented if at least one error is detected, and error signal producing means, through which at least one error signal is output when the value of at least one error counter exceeds a predeterminable limiting value (N1, N2, N3), wherein for at least one error counter, at least two different, predeterminable limiting values (N1, N2, N3) coexist simultaneously, and when each of these is exceeded by the counter reading (ik) of the at least one error counter, different error signals are output, and in response to the different error signals, different measures are carried out in the wheel-slip control system and/or wheel deceleration control system. 